Various aircraft utilize landing gear that is deployed for landing and retracted during take-off of the aircraft. The landing gear is housed within a compartment on the aircraft that is covered by a landing gear door. The landing gear door generally rotates 180 degrees during retracting and deployment of the landing gear. The landing gear door is hingedly connected to the aircraft and is supported by a rotation rod. One end of the rotation rod is fixedly secured to the aircraft while an opposing end of the rotation rod rotates 180 degrees during opening and closing of the landing gear door. During opening of the landing gear door the rotation rod is subject to compressive forces. During closing of the landing gear door the rotation rod is under tension.
Typically, rotation rods are manufactured from an aluminum alloy for weight reduction considerations. The rotation rods include a fixed segment having a main bore extending partially into a first end thereof. A second end of the fixed segment has a fastening device such as a rod end and bearing secured thereto. An opening of the main bore may include a threaded area configured to receive a threaded plug having another bore extending therethrough. The rotation rod also includes a rotatable segment. The rotatable segment has a cylindrical bearing member secured to a first end thereof. The rotatable segment has fastening device such as a rod end and bearing secured to a second end thereof, for securing the rotation rod to the landing gear door. The cylindrical bearing member defines a radially outer surface that extends between a first axial end and a second axial end thereof which rotate relative to complementary surfaces in the main bore. Typically, sleeves and or bushings (e.g., metallic or plastic sleeves or bushings) are employed between the bearing member and the complementary surfaces in the main bore to reduce friction and to serve as a sacrificial wear member. A lubricant, such as grease, is typically employed in the bore to further reduce friction and wear between the bearing member and the complementary surfaces in the main bore. However, such rotation rods generally require periodic maintenance to maintain proper lubrication and/or to refurbish or replace the sleeves and/or bushings.
Attempts to employ self-lubricating polymers in place of the metallic sleeves or bushings has been unsuccessful because such polymers fail (e.g., plastically compress or deform) under compressive forces. In addition, the polymers have a high coefficient of friction especially when slidingly engaging materials such as aluminum alloys. The coefficient of polymers on aluminum alloys increases with decreasing contact pressure. Typically rotation rods have cylindrical bearing members with large surface areas to reduce contact pressures and wear. However, the coefficient of friction of polymers on aluminum alloys increases with decreasing contact pressure. Thus, those skilled in the relevant art have been discouraged from employing polymers for lubricants on rotation rods.
A prior art greased type rotation rod assembly 200 is shown in FIG. 12. The prior art greased rotation rod assembly 200 includes a fixed member 220 having an annular first body portion 222 and a second annular body portion 224. The second annular body portion 224 has an inner surface 226 defining a bore 228 axially extending partially into the second annular body portion 224. The prior art greased rotation rod assembly 200 includes a rotatable member 240 having a piston section 242 extending from a linkage arm 244. The piston section 242 is rotatingly secured in the bore 228, as described herein. The piston section 242 defines a first lobe 242A and a second lobe 242B separated from one another and connected to one another by a shaft 245. The first lobe 242A defines a first axially facing annular bearing surface 242X; and the second lobe defines a second axially facing annular bearing surface 242Y.
The piston section 242 has an opening 242Q at a terminal end thereof that is positioned in the bore 228. The opening 242Q extends axially into an interior area 242R of the piston section 242 and terminates at an inside end surface 242D.
The prior art greased rotation rod assembly 200 includes a plug 234 removably secured (e.g., the plug has male threads) and is threaded into a portion of the inner surface 226 (e.g., a female threaded portion). The plug 234 defines a passage 234P that extends axially therethrough. The rotatable member 240 extends through the passage 234P and is axially restrained by the plug 234 which as an axial end 238. A plurality of holes H extend radially outward through the piston section 242 from the interior area 242R to the bore 228. The prior art greased rotation rod assembly 200 includes a first sleeve 241 positioned between the first lobe 242A and an axial internal end 236 of the bore 228. The first sleeve 241 has an L-shaped cross section with an axially extending flange that defines a first flange bearing surface 241A. The first flange bearing surface 241A is in rotational sliding engagement with the first axially facing annular bearing surface 242X.
The prior art greased rotation rod assembly 200 includes a second sleeve 243 positioned between the second lobe 242B and plug 234. The second sleeve 243 has cylindrical cross section and an inwardly facing axial end that defines a second bearing surface 243A. The second bearing surface 243A is in rotational sliding engagement with the second axially facing annular bearing surface 242Y.
The prior art greased rotation rod assembly 200 also includes an opening 247 (e.g., a zerk fitting) for injecting a supply of a lubricant such as grease or oil into the bore 228. The grease injected into the opening tends for flow through the interior areas 242R and through the holes H into the bore 228 as indicated by the arrows P. However, the grease tends to short circuit between a radially inner surface of the second sleeve 243 and an outer surface 242K of the piston section 242 as indicated by the arrows P1. As a result, the second bearing surface 243A that is in rotational sliding engagement with the second axially facing annular bearing surface 242Y does not get a sufficient supply of grease and prematurely wears.
Thus, there is a need for an improved greased lubrication rod assembly.